Preheat the oven to 350F and grease and flour a 9 inch springform pan.
To make the streusel topping, blend the bits of butter into the flour, sugar, and nuts until the butter is incorporated and the mixture has a coarse crumbly texture. I do this in my food processor. Put in the refrigerator.
Cream together the butter and sugar until light and fluffy. Beat in the eggs, one at a time and then the vanilla.
Peel and slice the peaches and sprinkle with lemon juice. Set aside.
Whisk together the flour, baking powder, cinnamon, salt, and nuts. Fold the dry ingredients into the butter/sugar mixture, along with the buttermilk.
Spoon the batter into your prepared pan, and smooth out evenly. Top with the sliced peaches, and then the streusel topping. Note: no need to arrange the peaches perfectly, but try to get them in an even layer.
Bake for about 50 minutes or until the top is lightly browned and a toothpick comes out without wet batter clinging to it (moist crumbs are ok!)
Let cool a bit in the pan before removing. Enjoy warm or at room temperature.
Notes
Leftover cake can be stored at room temperature loosely covered with foil or under a cake dome for several days. It can also be refrigerated.To freeze your cake: cool completely, then wrap in plastic and again in foil. Plan to use within 3 months.